The preparation of flocked rubber articles wherein flocks are fixed to the surface of the rubber material through an adhesive layer such as a polyurethane are well known. In such processes, the rubber surface is coated with a layer of the adhesive and short staple fibers are applied perpendicularly thereof utilizing an electrical field. The resulting electrostatically flocked articles are characterized by a fabric-like surface of relatively low friction. This feature renders flocked rubber articles particularly suitable for the purpose of reducing friction between the sliding glass window and window channel of automobiles. In view of the mechanical stresses involved in this application, it is imperative that the adhesive used to bond the flock to the rubber should contain components which not only bond to the flock but also to the rubber substrate. To this end, prior art flock adhesives comprised of isocyanate-functional urethane prepolymers have been improved by the inclusion therein of minor amounts of epoxy resins and aromatic nitroso compounds. Unfortunately, these adhesive compositions are unstable and moisture sensitive and exhibit a reduced open time. Consequently, they often lead to a gumming-up of adhesive application equipment. Attempts have been made to alleviate the moisture sensitivity and instability properties that plague isocyanate adhesives by blocking the isocyanate functionalities with blocking agents. While these attempts have been successful in many instances, it has always been at the expense of adhesive strength.
It is an object of the present invention, therefore, to improve flock adhesive compositions with respect to moisture and heat stability without adversely affecting adhesive strength.
Another object of the present invention is to prepare flocked rubber articles using a flock adhesive composition containing a blocked urethane prepolymer improved with respect to moisture and heat stability while simultaneously improving its adhesive strength.
Yet another object of the present invention is to provide a blocked urethane prepolymer of improved open time.
A further object of the invention is to provide a urethane adhesive composition reduced in free isocyanate content thereby minimizing the adverse environmental effects that characterize isocyanate adhesives.